Disable Fomantic's custom scrollbars (go-gitea#14109)

We already have custom scrollbars in our own CSS which are superior to
Fomantic's so diable them to save a few bytes and prevent interference.

web_src/fomantic/_site/globals/site.variables

@@ -3,3 +3,4 @@
 @headerFont: var(--fonts-regular);
 @pageFont: var(--fonts-regular);
 @bold: 500;
+@useCustomScrollbars: false;

web_src/fomantic/build/semantic.css

@@ -7723,22 +7723,6 @@ a.inverted.ui.card:hover,
 
 /* Scrollbars */
 
-.ui.dimmer:not(.inverted)::-webkit-scrollbar-track {
-  background: rgba(255, 255, 255, 0.1);
-}
-
-.ui.dimmer:not(.inverted)::-webkit-scrollbar-thumb {
-  background: rgba(255, 255, 255, 0.25);
-}
-
-.ui.dimmer:not(.inverted)::-webkit-scrollbar-thumb:window-inactive {
-  background: rgba(255, 255, 255, 0.15);
-}
-
-.ui.dimmer:not(.inverted)::-webkit-scrollbar-thumb:hover {
-  background: rgba(255, 255, 255, 0.35);
-}
-
 /*******************************
             States
 *******************************/
@@ -39175,53 +39159,6 @@ input::selection {
   color: rgba(0, 0, 0, 0.87);
 }
 
-/* Force Simple Scrollbars */
-
-body ::-webkit-scrollbar {
-  -webkit-appearance: none;
-  width: 10px;
-  height: 10px;
-}
-
-body ::-webkit-scrollbar-track {
-  background: rgba(0, 0, 0, 0.1);
-  border-radius: 0;
-}
-
-body ::-webkit-scrollbar-thumb {
-  cursor: pointer;
-  border-radius: 5px;
-  background: rgba(0, 0, 0, 0.25);
-  -webkit-transition: color 0.2s ease;
-  transition: color 0.2s ease;
-}
-
-body ::-webkit-scrollbar-thumb:window-inactive {
-  background: rgba(0, 0, 0, 0.15);
-}
-
-body ::-webkit-scrollbar-thumb:hover {
-  background: rgba(128, 135, 139, 0.8);
-}
-
-/* Inverted UI */
-
-body .ui.inverted:not(.dimmer)::-webkit-scrollbar-track {
-  background: rgba(255, 255, 255, 0.1);
-}
-
-body .ui.inverted:not(.dimmer)::-webkit-scrollbar-thumb {
-  background: rgba(255, 255, 255, 0.25);
-}
-
-body .ui.inverted:not(.dimmer)::-webkit-scrollbar-thumb:window-inactive {
-  background: rgba(255, 255, 255, 0.15);
-}
-
-body .ui.inverted:not(.dimmer)::-webkit-scrollbar-thumb:hover {
-  background: rgba(255, 255, 255, 0.35);
-}
-
 /*******************************
         Global Overrides
 *******************************/